1. Field of the Invention
The present invention broadly pertains to an orthodontic composition. More particularly, this invention pertains to an orthodontic adhesive that contains polymeric fillers.
2. Description of the Related Art
Orthodontic therapy is a specialized type of treatment within the field of dentistry associated with the supervision, guidance and correction of malpositioned teeth into proper locations. Orthodontic treatment can be useful in correcting defects in a patient's bite (also called occlusion) along with promoting better hygiene and improving the overall aesthetics of the teeth.
Orthodontic treatment often involves the use of tiny slotted appliances known as brackets, which are generally affixed to the patient's anterior, cuspid, and bicuspid teeth. After the brackets have been placed on the teeth, an archwire is received into the slot of each bracket and acts as a track to guide the movement of respective teeth to orthodontically correct positions. End sections of the archwire are typically received in appliances known as buccal tubes that are affixed to the patient's molar teeth. The combination of brackets, archwires, and buccal tubes is commonly referred to as an orthodontic brace, or “braces”.
It is common practice for orthodontists to use adhesives to bond orthodontic appliances to the surface of the tooth. This may be accomplished using a direct bonding method, which involves applying an adhesive to the appliance base, mounting the appliance to a tooth, removing any excess adhesive flash that has been extruded out along the base of the appliance, and finally hardening the adhesive. Alternatively, an indirect method may be used, in which appliances are first adhesively bonded to a replica of the patient's teeth (commonly made from plaster or orthodontic stone) and a resilient transfer tray formed over the appliances and the replica. The transfer tray is then used to carefully detach the appliances from the replica and re-bond the appliances simultaneously to the teeth of a patient, again using an appropriate adhesive. A variety of adhesives are available to the clinician for bonding appliances to tooth surfaces, and many offer excellent bond strengths. High bond strengths are desirable for maintaining adhesion of the appliance to the tooth surface over the duration of the treatment process, which can typically be two years or more.
At the conclusion of orthodontic treatment, all of the appliances are debonded from the teeth of the patient. There are also situations, however, in which appliances are removed from teeth prior to the conclusion of treatment. For example, the orthodontist may remove and re-position just one or two appliances in the middle of treatment to achieve a particular treatment goal. It is also possible that one or more appliances may become accidentally debonded when the patient bites down on a hard food substance.
In each of the above situations, some amount of residual adhesive is usually left on the tooth surface where the appliance was debonded, and this adhesive should be meticulously removed by the dental professional. Conventional orthodontic adhesives are highly crosslinked and usually contain hard inorganic fillers, such as silica. Moreover, these fillers are often present in amounts exceeding 50 weight percent of the adhesive in order to achieve high strength and acceptable adhesive handling properties. Once hardened, these materials tend to be difficult and time-consuming to remove from the patient's teeth. Presently, the removal process often involves the use of a hand tool with a rotating tip such as a fluted tungsten carbide burr operating in the range of 20,000 to 200,000 rpm. Because tungsten carbide is a relatively hard material compared with tooth enamel, there is some risk that the tip will accidentally cause enamel damage, and as a result this removal task is generally carried out by the orthodontist and not delegated to assistants.
Grinding adhesive from the tooth takes a substantial amount of time and it is often cited as one of the most cumbersome procedures, for both orthodontist and patient, of the entire orthodontic treatment. Furthermore, since the orthodontist's time is very valuable relative to an assistant's time, any procedure only carried out by the orthodontist is inefficient from a financial and/or office management standpoint.
There are also other risks associated with using a high speed rotary hand tool on a patient. High rotation speeds cause frictional heating of the enamel surface by the fluted burr. Although this heating can be alleviated using a stream of coolant water, many clinicians avoid using such a coolant because it is often easier to see remnant adhesive on the enamel when the site is dry. Recent studies suggest that the temperature rise in the pulpal chamber caused by grinding using a fluted burr may be as high as 9.5° C. if a 6-fluted carbide burr is used (Jonke et al. World Journal of Orthodontics, Vol. 7, p. 357 (2006)). Tooth pulpal damage can occur at these temperatures (Zach et al. Oral Surg. Oral Med. Oral Pathol. (1965) Vol. 19, pp. 515-530).
Some references have suggested using lower amounts of filler in an orthodontic adhesive than the amounts typically used, to ease removal of residual adhesive. Some of these concepts are described in Gwinnett and Gorelick, Am. J. Orthod., Vol. 71, No. 6, pp. 651-665 (June 1977), Retief and Denys, “Finishing of Enamel Surfaces After Debonding of Orthodontic Attachments”, Angle Orthodontist, Vol. 49, No. 1, pp. 1-10 (January 1979), and U.S. Pat. No. 3,629,187 (Waller, et al.). However, removal of residual adhesive containing these fillers still can lead to enamel damage because hardened tools must be used to grind away the residual adhesive. Clearly, any damage to the pulp of the tooth should be avoided if possible.